The present invention relates to an electromagnetic deflection type picture tube device which ensures better resolution over the whole surface of a screen.
In general, picture tubes like television picture tubes which reproduce relatively large images have a wide screen and a wide deflection angle of electron beam, so that the electromagnetic deflection system of high deflection efficiency is employed. In order to reduce distortions of images to a minimum or in order to attain a higher degree of convergence of three electron beams over a screen, the deflection field is suitably distorted that is, the distribution of a deflection field is varied. For instance, in the case of the in-line self-convergence type color picture tube, the horizontal deflection field is imparted with a strong pincushion distortion while the vertical deflection field, with a strong barrel distortion so that the three electron beams are correctly converged especially at the edges of a screen.
However, the prior art in-line self-convergence systems are all not satisfactory in their performance in practice that is, they cannot attain a satisfactory degree of resolution.